dt-bindings: net: dsa: qca8k: Add SGMII clock phase properties

Add names and descriptions of additional PORT0_PAD_CTRL properties.
qca,sgmii-(rx|tx)clk-falling-edge are for setting the respective clock
phase to failling edge.
Co-developed-by: Matthew Hagan <mnhagan88@gmail.com>
Signed-off-by: Matthew Hagan <mnhagan88@gmail.com>
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/dsa/qca8k.txt

@@ -37,6 +37,10 @@ A CPU port node has the following optional node:
                           managed entity. See
                           Documentation/devicetree/bindings/net/fixed-link.txt
                           for details.
+- qca,sgmii-rxclk-falling-edge: Set the receive clock phase to falling edge.
+                                Mostly used in qca8327 with CPU port 0 set to
+                                sgmii.
+- qca,sgmii-txclk-falling-edge: Set the transmit clock phase to falling edge.
 
 For QCA8K the 'fixed-link' sub-node supports only the following properties: